He has been held in an unknown location, denied access to a lawyer and was only charged on Wednesday.

In a statement, Chinese authorities said Mr Liu had been "engaged in agitation activities, such as spreading of rumours and defaming of the government, aimed at subversion of the state and overthrowing the socialism system in recent years".

Roseann Rife, Amnesty's deputy program director for Asia and the Pacific, told Radio Australia's Connect Asia program Mr Liu could face years in jail.

"This is yet again ... using state security charges simply to silence people who are expressing opinions that the state doesn't like," she said.

Ms Rife says Mr Liu was being punished for trying to urge reform.

Mr Liu was detained earlier, in 1989, when he was put in jail for 20 months after the Tiananmen Square protests.